The present invention relates to an electron beam source for use in electron microscopes and electron beam inspection and measuring apparatus for evaluating and inspecting semiconductors integrated circuits, electron beam lithography systems for depicting circuit patterns on semiconductors, and the like. Particularly, the present invention relates to a method for processing materials of electron emitting devices for use in electron beam sources.
When a material for use in an electron beam source is manufactured, conventionally, the manufacturing has been mostly performed without regard to the to the crystal direction of the material. A method for obtaining a needle shaped electron emitting material having a curvature of equal to or less than 50 nm by forming a needle like end portion of a crystal rod or a crystal bar utilizing a cleavage plane, and subsequently performing an anisotropic etching has been disclosed in JP-A-5-101770 (1993). However, the prior art discloses a method for obtaining a field emission type cathode which is operable with the lowest voltage than ever before, and the prior art does not teach how to utilize the cleavage plane of the material in manufacturing.
FIGS. 2(a), 2(b), and 2c illustrate a conventional manufacturing method for an electron beam source. FIG. 2(a) is a plan view of a crystal bar, i.e., a material for manufacturing, FIG. 2(b) is a plan view and a side view of a chip base material 2 cut out from the crystal bar, and FIG. 2c is a plan view and a side view of a chip 3 cut out from the chip base material 2.
In accordance with FIG. 2(a), the crystal bar 1 has an axial direction 4 of its mechanical axis and an axial direction 5 of its crystal axis in the process of manufacturing, and the directions of the mechanical and crystal axes do not coincide each other. The end plane of the crystal bar 1 is tilted with respect to the axial direction 4 of the mechanical axis, and the end plane is a cleavage plane of the crystal. Conventionally, the chip base material 2 was cut out from the crystal bar 1 by cutting perpendicularly to the mechanical axis of the crystal bar 1 with a designated length, and the chip 3 was also cut out from the chip base material 2 in a manner that the longitudinal direction of the chip is the same as the mechanical direction 4 of the crystal bar 1. When the chip cut out in the manner described above is manufactured, the axial direction 4 of the chip 3 does not coincide with the crystal direction 5 of the chip 3.
FIG. 3 is a schematic side view of an electron emitting device 6 manufactured from the above chip 3, which is used by being attached to an electron beam source of the above-mentioned electron microscope, electron beam inspection and measuring apparatus, electron beam lithography system, and the like. The chip 3 is a rectangular solid as shown in FIG. 2(c), and the chip is manufactured into an electron emitting device 6 having a shape shown in FIG. 3. An end of the electron emitting devise 6 is formed as a hemispherical portion 61 for emitting electrons, and another end is a fixing portion for attaching to the electron beam source. The electron emitting device 6 is attached to the electron beam source so that the axial direction (shown by a one dot chain line) of the device coincides with the axial direction of the electron beam of the apparatus, and the electron beam is emitted from the hemispherical portion 61 of the electron beam emitting device 6 by applying a voltage.
In the above apparatus, not only the intensity and energy of the electron beam, but also uniformity of electron irradiation in a plane of the material, to which the electron beam is irradiated, must be controlled. When the electron emitting device 6 manufactured by the conventional method shown in FIG. 2 is used, the emitted electrons are not axially symmetrical to the axial direction 4, because the axial direction of the electron emitting device 6 does not coincide with the crystal direction 5. This results in a problem because the emitted electron distribution is not axially symmetrical.
FIG. 10 indicates a spread of an electron beam seen from the electron beam source when an electron beam is irradiated onto a specimen. For instance, in an electron beam lithography system, the size of the spread of the irradiated electron beam must be changed depending on the pattern to be depicted. The region A in FIG. 10 indicates the ordinary size of an irradiation field of the electron beam, and the region B indicates an extended field of the electron beam. When an electron emitting device 6 processed by the above conventional manufacturing method is used, the region B becomes not a circle but an ellipse, because the axial direction of the electron emitting device 6 does not coincide with the crystal direction 5. Accordingly, an effective region of beam for writing becomes a rectangle inscribed in the ellipse, which is smaller than a rectangle inscribed in a circle, as described in more detail below.